Boards provided with cover layers on both sides, such as gypsum board and foam boards made of polystyrene, polyurethane or urea-formaldehyde resins are widely used as structural components such as roof elements and for thermal and acoustical insulation, and as packing material.
These materials are today produced to a very great extent in a continuous process in so-called board plants in which the foaming is performed between revolving board belts, while the core material or its formation from liquid components, as for example in the case of polyurethane foam, is shaped against these revolving board belts. To prevent adhesion to these revolving board belts, paper layers accompany the upper and lower board belts in contact therewith. These layers bond to the core material, i.e., the polurethane foam for example, and usually also remain on them as bilateral cover layers, because the board thus made thereby gains stability and strength, and also the surface quality improves. It has already been proposed to use webs of matting or fabric as cover layer materials, such as mats or fabrics of cellulose fibers, polyester fibers and, glass fiber mats or fabrics on account of their incombustibility. Another advantage of such cover layers of matting or fabric consists in the fact that the core material, such as the polyurethane foam, is able to penetrate the interstices present in them and thus a good anchoring between core material and cover layer material is assured. The bond between core and cover layer material of paper or film has always been problematical. Nevertheless, matting and fabric materials have not succeeded as cover layer material, because the liquid components penetrate through the interstices present in the matting or fabric and result in adhesion to the board bands. Such liquid or liquid-containing starting components are present especially in the manufacture of PU hard foams, but also in urea-formaldehyde foam materials in which the starting materials set or react chemically, and in the manufacture of gypsum boards which set hydraulically.
An attempt has been made to remedy this disadvantage by coating the matting or fabric materials with polyethylene or bitumen, it being necessary in the latter case to sprinkle the cover layer additionally with sand to enable it to be handled. It is disadvantageous in these known materials, however, that both polyethylene and bitumen penetrate rather strongly into the matting or fabric, which thereby loses its open structure, and the bond between matting or fabric and the core of the material forming the board thus becomes insufficient. In the case of PU hard foam boards, on the example of which the invention is described below, there is another disadvantage in the fact that both materials are easily combustible, and thus the PU hard foam board made therefrom and provided with cover layers has extremely poor properties with regard to its behavior wh.
Therefore there exists an urgent technical need for a cover layer material which does not have the disadvantages indicated above, which permits the continuous production of boards from liquid starting components without passing through the matting or fabric and sticking to the boards or webs. Such a cover layer material is furthermore to conform in its behavior in contact with fire as closely as possible with building material group B2 or B1, but if possible even with building material group A2. It is furthermore to be resistant to hot bitumen, so that the cover layer will not be destroyed by the tarring so frequently performed on flat roofs, for example, and so that no formation of blisters, i.e., partial separation between the cover layer and PU hard foam, will occur.
This problem is solved by a cover layer material with the distinguishing features of the patent claim, which is characterized by the fact that the matting or fabric has on one side a coating of 70 to 94 wt.-% of a powdered inorganic material and 5 to 30 wt.-%, absolutely dry, of a binding agent; preferably the powdered inorganic material in the coating composition amounts to even 80 to 94 wt.-%, absolutely dry, of the total coating.
In DE-OS No. 31 20 342, with the object of achieving fire retardancy, an insulation body is described which has an outer skin composed of glass fiber matting and bearing a coating of at least one metal oxide such as aluminum hydroxide and/or antimony oxide and plastic copolymers. The requirements specified for the invention and set forth above cannot be satisfied by the technical teaching of this prior disclosure nor is the invention suggested by it. The content of metal oxide in the dried composition is between 50 and 70 wt.-%, the coating composition being applied in a pasty, foamed state to the glass fiber matting and then dried by radiant heat. Such a coating composition may satisfy the requirement of fire retardancy, but it does not provide the solution of the problem addressed herein. In the case of percentage contents of 50 to 70 wt.-% of inorganic material, these are concentrations of solids as they are commonly used in brushing and coating compositions. For the purpose pursued by the invention, such common coating compositions, with a high content of binding agent and liquid, are not suitable because liquid and binding agent strike through the matting or fabric and lead to the feared adhesion to the board belts of the continuous board machine. The considerable amounts of liquid to be removed also lead to bubbles and shrinkage in the drying process and the coating does not dry free of cracking.
For this reason a preferred method of producing the cover layer material consists in the use of a coating composition with a very high solids content, preferably of 70 to 80 wt.-%. Surprisingly, this coating can still be applied with a backfilling machine. It is best dried with hot, recirculating air and results in a perfectly impermeable coating without bubbles, shrinkage or cracking.
The advantage of the cover layer material according to the invention lies in the fact that, due to the unusually high content of inorganic material, the matting or fabric becomes impermeable to the liquid starting components, so that the open structure of the matting or fabric is preserved and good anchoring of the cover layer material to the core material of the plate during the later shaping and foaming is assured.
The high content of inorganic material furthermore brings it about that a PU hard foam web provided with this cover layer material is resistant to hot bitumen at, for example, 180.degree., the cover layer is not destroyed and no bubble formation occurs between cover layer and PU hard foam. Moreover, the high content of inorganic material further reduces inflammability below that of previously known materials.
The binding agents can be not only those on an inorganic basis, such as water glass, but also those on an organic basis, especially on a plastic basis. Since water glass as binding agent makes the cover layer rather brittle, mixtures containing binding agents of a plastic basis are also recommendable. In organic binding agents have the advantage that they further reduce inflammability.
The binding agents on the basis of plastic are preferably used in the form of plastic dispersions with a solids content of 35 to 70% by weight. They include especially polyvinylidene chloride and polyvinyl chloride, which have the advantage of being fire retardant, and copolymers and terpolymers of vinyl acetate with maleic acid and acrylic acid. Especially preferred on account of their good binding agent properties in comparison with the organic coating components, styrene-butadiene copolymers and polymers or copolymers of acrylic acid and methacrylic acid, respectively. The amount of plastic dispersion to be used depends to some extent on the solids content, and, to keep the energy required for the drying of the coating low, dispersions of the highest possible solids content are used.
The greatest variety of powdered substances are suitable as inorganic material, especially those on a mineral basis, such as silicates, clays etc. On account of its easy availability, calcium carbonate has proven to be especially preferred.
For the achievement of better values in relation to behavior on exposure to fire ["Brandverhalten"] aluminum hydroxide or alumina trihydrate is recommendable as an inorganic material, with which a fire retardancy rating of A2 can be achieved.
To remain economical, in a preferred embodiment of the invention the inorganic material consists of a mixture of 10 to 50 weight-percent of calcium carbonate and 90 to 50 weight-percent of aluminum hydroxide or alumina trihydrate. In this case, the higher the content of the aluminum hydroxide or the alumina trihydrate content is, the more fire-retardant the cover layer material and the PU hard foam board covered with it becomes.
It is desirable for the coating also to contain certain percentages of organic or mineral colorants for the purpose of distinguishing different quality classes of the board, for example with regard to fire retardancy. To counteract the translucency of the cover material and prevent light from showing through the often yellowish PU hard foam, coloring the cover material with carbon black has proven to be preferable, because even small amounts cover large areas.
For special applications, especially when a white cover layer material and thus a white PU hard foam board or white gypsum board is desired, the admixture of up to 5 weight-percent of titanium oxide powder, with respect to the total amount of inorganic material, has proven to be preferable.
The matting or fabric used for the cover layer material can best have a specific weight between 35 and 350 g/m.sup.2, preferably from 40 g/m.sup.2 to 150 g/m.sup.2, and the applied weights of the coating are best between 150 and 450 g/m.sup.2, these weights being dependent to a great extent on the application, the thickness of the core material, and other such factors. Glass fiber matting and fabric material has proven especially desirable as matting and fabric material, since it is incombustible. A matting and fabric material on a cellulose basis is desirable for use as a matting and fabric material on an organic basis. On account of its good strength rating, a polyester fiber matting is preferentially suitable. In the case of cover layer material for gypsum boards, it is desirable to use both nonwoven and woven fabrics together, because in this manner the liability to breakage of the gypsum boards can be very substantially reduced. Quite generally, the use of matting and woven fabric together can considerably increase the longitudinal and transverse strength.
Especially preferred is the use of the cover layer material according to the invention for the production of boards provided with cover layers on both sides in a continuous board producing plant using a top and bottom belt. It is also, of course, suitable for use as a laminating material for lamination, for example, onto polystyrene foam boards cut from a block of foam polystyrene, and here again the uncoated side of the matting or fabric is available for a good bonding of the cover layer material to the core material through the laminating material.